1. Field of the Invention
The present invention relates to current to pressure transmitter apparatus.
2. Prior Art
Various electro pneumatic transducers which convert a current signal into a pressure signal for controlling valves and the like have been advanced. For example, Fischer Controls of Marshalltown, Iowa makes several models, typical of which is the Type 456 Electro Pneumatic Transducer. However, these devices provide for a control pressure which utilizes an armature for controlling a gas flow, and which gas flow in turn operates a feedback diaphragm controlling the bleed of a supply of gas under pressure to atmosphere.
An additional type of device which operates on a similar principle, but which uses mechanical feedback is called the E69 Series Current Pneumatic Converter Positioner made by the Foxboro Company of Foxboro, Mass.
Certain prior art current to pressure converters use a type of a flapper valve controlling a flow from a nozzle, and the use of a piezoelectric crystal as a flapper has also been known in the prior art. U.S. Pat. No. 3,456,669 illustrates a piezoelectric flapper valve, operating in a transducer for providing current to pressure conversion. However, in this situation, the flapper valve controls the exhaust of fluid from a chamber. An additional piezoelectric bender element used for controlling pressure outflow from nozzles is shown in U.S. Pat. No. 3,063,422.
A control element using a flapper controlling nozzle pressure output is shown in U.S. Pat. No. 2,914,076, and a bellows in this device operates a rheostat for providing a signal indicating the pressure of the fluid being controlled.
An additional control apparatus using fluid pressure signals is shown in U.S. Pat. No. 2,928,409. Typical other examples of this type of device include U.S. Pat. Nos. 2,939,430 and 3,134,425.